yeah get a new one aimed at gamers--that ones just a plain old mouse with a low dpi
i use a 12 inch by 12 inch linoleum floor tile for a mouse mat--works great and only cost me £1 in a local diy shop --been using it 5 years now and its still as good as new--a bit of furniture polish on it now and then keeps the mouse gliding smooth as silk on it
I don't know if a new mouse will help you aim better, but a mouse that feels better in your hand will make it seem more fluid to move around. A decent mousepad can help as well. I use any old mouse pad as long as it remains smooth. If my mouse catches on anything, it's time for a new one.
Mice are one of those items that are SOO subjective and everyone will give you a different answer. They have mice geared to MMO games, FPS games, etc. My personal opinion is get a mouse that has general good reviews and will work well for your games. I used a Microsoft Intellimouse USB 1.1 for YEARS, I mean YEARS! It was the center of many temper filled moments and I think I smashed it with my fist one to many times. I am now sporting an Ideazon Reaper mouse. Steel Series actually bought Ideazon so I don't think they make these mice anymore. I see they are on Amazon for $40. I love it though. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
To keep the price down on a mouse, you might find an optical mouse cheaper than a laser mouse. Honestly I have never really seen a huge difference in either. Laser mice don't have the annoying bright red led light though as optical mice do.
Additional mice buttons are ALWAYS good to have. They put more than just a trigger at your fingertips.
A DPI button is also handy especially for games that demand increase sensitivity or speed. I find myself using a DPI button when I jump in a tank to speed up the turret movement. It's nice, but not necessary.
As far as recommended mice, the brand names mice like Logitech and Razer are going to be good. However, you also pay for the name. The Logitech G500 mouse is nice, but is $50 on Newegg. For $40 ($30 cash = $10 NE card), you may want to look at the odd brands. Just read reviews and see what you find. I got mine as a daily deal thing for $30.
^ nothing wrong with it. It will be a lower quality mouse from logitech, meaning it might feel light and cheaper than a gaming mouse. It has good reviews thought. It's completely your choice. Anything will be better than what you have.